1. Field of the Invention
The present invention relates to a method for automatically aligning horizontal rolls and vertical rolls in a universal rolling mill stand, particularly after the stand has been changed or converted to new types of sections in the rolling mill train. The alignment is effected by means of adjusting members and by means of position measuring devices for the roll adjustments which are connected to computing units and particularly take into consideration the spring characteristic constant. The invention also relates to an arrangement for carrying out this method.
2. Description of the Related Art
A method of the above-described type for the automatic alignment of the rolls of a universal rolling mill stand is described, for example, in German patent 35 01 622. In this known method, the lower roll is moved to the roll middle and the upper roll is moved with rolling pressure to the lower roll. By moving the rolls together, the respective positions of the rolls are determined, wherein the position of the lower roll in the roll middle is used as the initial value. The further method steps are oriented with respect to the lower roll aligned in this manner. In other words, the upper roll and the vertical roll are aligned relative to the lower roll in such a way that the axial fastening of the upper roll is released and the vertical rolls are moved in the direction towards the roll middle, whereby the vertical rolls may rest against a side of the upper roll and may axially displace the upper roll until both vertical rolls rest against the sides of the lower roll. The upper roll is then fixed in this position. All rolls are then subjected to rolling pressure and the system is set to zero in the connected computer. This known method for aligning the rolls does not take into account that the springiness of the stand in radial direction of the horizontal rolls and the springiness of the stand in radial direction of the vertical rolls may be very different. For this reason, the known alignment of the rolls is subjected to substantial inaccuracies which at the latest become a disadvantage when the stand begins to operate with the first sectional material to be rolled and the roll pressures are applied.
European patent application 0 248 605 describes a method for aligning the vertical rolls and the horizontal rolls of a universal rolling mill stand, wherein initially the upper horizontal roll is moved into a predetermined initial position in the roll gap middle and the two vertical rolls are moved against the sides of the upper horizontal roll in order to determine the initial position of the upper horizontal roll. Subsequently, the vertical rolls are moved back and the lower horizontal roll is moved against the upper horizontal roll in order to determine an initial position for the lower horizontal roll. Finally, the two vertical rolls are moved against the sides of the upper horizontal roll and of the lower horizontal roll. If the edges of the horizontal rolls are not in alignment after the above-described alignment has been carried out, the axial locking of one of the horizontal rolls is released and this horizontal roll is moved by the vertical rolls towards the aligned edge position. This European patent does not provide any indication with respect to the need for determining the springiness of the stand with respect to the horizontal rolls and the vertical rolls simultaneously with the alignment of the rolls, so that the geometric coordinates of the stand are reproducibly determined with respect to the rolled material or the rolled section. The European patent application does mention a coarse adjustment for the vertical rolls and an AGC-cylinder, however, the above-described necessity of a separate spring characteristic determination is not mentioned.
German Offenlegungsschrift 38 01 466 describes an adjusting device for a universal stand with electromechanical coarse adjustments and hydraulic fine adjustments for the roll. The adjusting device carries out a calibration process for the stand in time intervals. For this purpose, all rolls are electromechanically moved toward each other to reach zero pass and, subsequently, different average hydraulic pressures to be expected in accordance with the pass schedule are adjusted. All stored hydraulic pressures in the different position values of the fine adjustments result in the stand spring characteristic for the vertical and horizontal force pattern. The position and pressure values adjusted under calibrating conditions are set at zero value. The above-described measures make it possible satisfactorily to carry out the pass adjustments, particularly of the finishing stand in a universal beam rolling mill, without requiring a test run and a test bar.
The above-described known methods for aligning the rolls of a universal stand have the disadvantage that the roll positions determined in this manner in the stand cannot meet the practical requirements because, for example, in asymmetric sections, the determined vertical middle of the roll body is not identical with the shape of the pass. This necessarily results in unequal roll forces.